The present invention relates to improvements in portable combustion-powered tools, and particularly to a fuel injection system for such a tool.
Portable combustion-powered, or so-called IMPULSE brand tools for use in driving fasteners into workpieces are described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,552,162, 4,483,473, 4,483,474, 4,403,722, and 5,263,439, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Lincolnshire, Illinois under the IMPULSE.RTM. brand.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A powerful, battery-powered electronic power distribution unit produces the spark for ignition, and a fan located in the combustion chamber provides for both an efficient combustion within the chamber, and facilitates scavenging, including the exhaust of combustion by-products. The engine includes a reciprocating piston with an elongate, rigid driver blade disposed within a cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the ignition of a charge of gas in the combustion chamber of the engine, the piston and driver blade are shot downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or "ready" position through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
In some combustion-powered tools, such as that shown in U.S. Pat. No. 5,263,439, the fuel metering valve is located in or near the cylinder head, and as such is affected by heat radiated from the combustion of gases. The combustion chamber and the cylinder body become relatively hot due to this radiated heat. These relatively high temperatures can cause the premature vaporization of the pressurized MAPP fuel at the point of metering the fuel into the combustion chamber. Thus, since vapor, rather than liquid fuel is being metered, fuel volume decreases in the combustion chamber, combustion efficiency suffers accordingly, and the tool will fail to fire. After about 200 rapid fire successive shots, vapor lock often resulted.
Further, combustion-powered tools of this type are designed for use in stressful construction environments, and are often dropped on the ground or have other objects dropped upon them. In addition, construction sites are typically dusty, and although IMPULSE.RTM. tools do not require as frequent cleaning as powder activated technology (PAT) tools, it still costs approximately $100 per cleaning, and the operator loses the use of the tool while it is being cleaned. Thus, another design factor of such tools is that the sensitive internal components, such as the fuel metering valve, be protected from shock to extend the cleaning interval.
Another drawback of conventional combustion tools is that the location of the fuel metering valve in the cylinder head of the tool makes it difficult to route the valve control leads.
Accordingly, a first object of the present invention is to provide an improved combustion-powered tool wherein the fuel metering valve is isolated from the heat generated by the combustion chamber.
Another object of the present invention is to provide an improved combustion-powered tool wherein the fuel metering valve is protected from shock impact damage from both tool-generated cylinder impact forces and accidental handling damage.
A further object of the present invention is to provide an improved combustion-powered tool wherein incoming fuel is heated after passing through the metering valve and prior to its entry into the combustion chamber.
A still further object of the present invention is to provide air improved combustion-powered tool wherein fuel is introduced into the combustion chamber in a location from where it can be evenly distributed and may efficiently impact the spark plug.